1. Field of the Invention
The present invention relates to a golf ball comprising a core, an inner cover, and an outer cover, and more particularly to a golf ball having a mark portion for indicating, for example, a trademark, a number, a symbol, a figure, or a pattern, which is formed on the surface of the outer cover when the cover is molded.
2. Description of the Related Art
Most solid golf balls have had a two-layer (a two-piece) structure in which a single layer core is covered with a single-layer cover. In recent years, however, there have been proposed and marketed many kinds of multi-layer golf balls having three or more layers in which at least one of a core and a cover comprises two or more layers. A process of manufacturing such a multi-layer golf ball having three or more layers involves many manufacturing steps. For example, a three-layer golf ball comprising a core, an inner cover and an outer cover is manufactured through the steps of: (1) molding a core, (2) conveying the core to an inner cover injection stage, (3) placing the core into a hopper (a storage apparatus) for temporary storage, (4) injection molding an inner cover on the core, (5) conveying the core covered with the inner cover to an outer cover injection stage, (6) placing the core into a hopper (a storage apparatus) for temporary storage, and (7) injection molding an outer cover on the core covered with the inner cover.
A mark portion indicating, for example, a number or a trademark including characters or a figure is provided on the surface of a golf ball. The mark portion is generally formed by means of a decalcomania method in which, after a core has been covered with a cover, a decalcomania film printed on decalcomania paper is transferred, through heating and pressing, onto the mark-forming site of the surface of the cover.
The above-described process for manufacturing multi-layer golf balls having three or more layers is more complicated than a process for manufacturing conventional two-piece golf balls. Therefore, manufacturing cost increases.
Also, the process of forming a mark portion by means of the conventional decalcomania method requires an independent process of forming the mark portion after molding of a cover. Therefore, the process for manufacturing golf balls become complicated and thus involve disadvantages in terms of productivity and manufacturing cost. Japanese Patent No. 2904737 discloses a cover material for a golf ball which has eliminated the above-mentioned disadvantages. The cover material is formed by means of a multi-color injection molding process employing two or more kinds of molding materials of different colors, and has the shape of a hemispherical cup. A mark portion is formed on the outermost surface of the cover material by at least one of the molding materials. The cover material is used for compression molding of a cover.
However, in the above-mentioned cover material of Japanese Patent No. 2904737, the molding material forming the mark portion does not completely enclose a core. Thus, a golf ball manufactured from the cover material has a problem in which stress is apt to concentrate upon impact at the boundary between a molding material which forms the mark portion and another molding material which is in contact therewith. Therefore, the cover material leaves room for improvement in terms of durability of the mark portion and the ball itself.
The present invention has been accomplished in view of the above-mentioned circumstances, and an object of the present invention is to provide a multi-layer golf ball which comprises at least a core, an inner cover, and an outer cover; which can be produced in a simple manufacturing process; a mark portion of which can be formed without an independent formation process, so as to reduce manufacturing cost; and which is excellent in durability of the mark portion and the ball itself.
In order to achieve the above object, the present invention provides a golf ball which comprises at least a core, an inner cover, and an outer cover. The inner cover completely encloses the core, and the inner and outer covers are of different colors. A portion of the inner cover penetrates the outer cover and is exposed to the outside on the surface of the golf ball. The exposed portion constitutes a mark portion on the surface of the golf ball.
In the golf ball of the present invention, the inner and outer covers are molded in a single stage through use of an injection molding machine (described later) in which an inner-cover mold and an outer-cover mold are arranged on a common mold base. The inner cover is molded on the core by use of the inner-cover mold, and subsequently the outer cover is molded on the inner cover by use of the outer-cover mold. Also, the mark portion can be formed when molding the inner and outer covers, and therefore no independent process of forming the mark portion is necessary. That is, the golf ball of the present invention can be manufactured in a simple process comprising the steps of (1) molding a core, (2) conveying the core to a stage for injection molding of the inner and outer covers, (3) placing the core into a hopper for temporary storage, and (4) forming the inner and outer covers and the mark portion by injection molding, whereby manufacturing cost is reduced.
In the golf ball of the present invention, the inner cover completely encloses the core and the mark portion is formed by a portion of the inner cover. This structure prevents stress from concentrating upon impact at the boundary between the inner and outer covers, and excellent durability of the mark portion and the ball itself can be achieved. Further, because the mark portion is formed by a portion of the inner cover, the golf ball of the present invention has also an advantage of improved appearance, as compared with a ball whose mark is formed by means of the decalcomania method.